Download Analysis of Color Consistency in Retinal Fundus Photography:

Analysis of Color Consistency in Retinal Fundus Photography:
Application of Color Management and Development of a Eye
Model Standard
Christye P. Sisson, Susan Farnand, and Mark Fairchild, Rochester Institute of Technology, and Bill Fischer, University of Rochester
Medical Center, Flaum Eye Institute (USA)
Background
Color variation in retinal fundus photography represents a
significant gap in the standardization of color for fundus
cameras. Fundus cameras are used in in the context of
ophthalmology as a method of documenting a patient’s retina to
monitor pathology over time. This form of ophthalmic imaging
is also used in clinical trial research and increasingly, teleophthalmology, as a stand in for an in-person examination.
Given the increased reliance on these images as representation’s
of the appearance of a patient’s eye, it becomes important to
identify inconsistencies between devices and provide the most
accurate rendering of the retina possible.
This research aims to identify these inconsistencies and
reconcile them by proposing an eye color model standard. The
authors could not identify other attempts to reconcile retinal
color at capture, only after the fact image adjustment (Hubbard,
et al) or application of current color management practices
(Bull). Figure 1. Examples of the variation of color among fundus images of the same retina.
Method
The method for both documenting and reconciling the color
inconsistency in fundus cameras included photographing a
standardized color target (ColorGauge Pico Target)*, inside a
model eye with a standardized imaging protocol. Fundus
cameras operate by projecting a donut of light from the lens
through a dilated pupil to illuminate the retina. The model eye
was utilized to mimic the imaging conditions of the eye as the
other half of the optical system. After capturing on several
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*ColorGauge Pico Target is available from Image Science Associates
22nd Color and Imaging Conference Final Program and Proceedings and 2nd Congress of the International Academy of Digital Pathology
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fundus camera systems, the images were exported as TIFFs and
compared to the original color targets. Colormetric profiles for
each camera were generated and applied back to the images to
determine how closely the images could be made to match each
other.
Results
The testing showed significant color variation among 8
tested cameras, even among those from the same manufacturer.
The resulting targets also demonstrated significant variation in
contrast among the cameras tested. This is not unexpected given
the cameras variety in terms of bit depth and sensor type, but we
have not determined if these variations are products of the
hardware and not part of the color and gamma correction applied
at the imaging system software level by the manufacturer.
The application of individually generated camera profiles
brought the color variations into much greater levels of
agreement in the majority of cameras tested. Cameras that
“failed” most often included those that were very high contrast,
demonstrated by the greyscale patches in the target.
Consequently, the color data in these images was much more
limited, making it more difficult to bring the color into
agreement with the original target.
Figure 2. Six of the tested cameras test target images.
Conclusion
The testing confirmed the wide disparity in color
consistency and accuracy among fundus camera systems. The
color variations between the tested cameras were successfully
mitigated by the application of the profile to the final images in
most cases. However, the question remains if the color variation
exists in the hardware of the cameras or in the image
modifications that occur at the software level, or both. In either
case, the testing demonstrates that it is possible to bring cameras
from a wide variety of manufacturers within greater color
agreement than was previously displayed.
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References
[1]
[2]
[3]
Hubbard, L. “Digital Color Fundus Image Quality: The Impact of
Tonal Resolution”. Journal of Ophthalmic Photography. Volume
31, Number 1. (2009): 15--‐20. Print.
Hubbard, L. Ferris, F. “Digital Color Retinal Imaging”. Journal of
Ophthalmic Photography. Volume 31, Number 1. (2009): 6--‐7.
Print.
Bull, L. “Color Management for Ophthalmic Fundus
Photography”. Journal of Ophthalmic Photography. Volume 31,
Number 1. (2009): 40--‐44. Print
© 2014 Society for Imaging Science and Technology